1. Field of the Invention
The invention relates to display devices, and more particularly, to a digital filtering device of the display devices.
2. Description of the Prior Art
When a display device displays an image represented by an analog video signal, the distortion of the video signal may cause problems, for example, the image displayed by the display device has noises, or the image is indistinct. There are some typical indistinct phenomena of the image, for example, within the image, a black dot is not black enough, and a white dot is not white enough, which are probably caused by the smear effect over the video signal, where effects of this kind are usually referred to as the pulse smear effect. If a video object within the image has a vertical edge and the edge seems to be dragged, the dragged edge phenomenon may also be caused by the smear effect, where effects of this kind are usually referred to as the edge smear effect. In addition, if a video object within the image has a vertical edge and the edge seems to be repeated around, the typical reasons causing the repeated edge phenomenon may include the overshoot effect of the video signal, the undershoot effect of the video signal, or the ringing effect of the video signal.
One of typical reasons causing the distortion of the video signal is the frequency response of the circuitry of the display device. If the frequency response is low pass, the smear effect mentioned above may easily occur. On the other hand, if the frequency response is high pass, the overshoot/undershoot effect mentioned above may easily occur, where the ringing effect is usually introduced after the overshoot/undershoot effect.